Can air pollution affect heart health?

Can air pollution affect heart health?

­Scientists have long known that air pollution causes health problems. Most attention has focused on lung issues like asthma, lung development in children and even lung cancer. It makes sen­se: When air is infused with harmful chemicals like sulfur dioxide, carbon monoxide and hydrocarbons, along with tiny particles of matter, our lungs are going to suffer.

These pollutants come from lots of sources, some natural, like volcanic eruptions and plants' chemical reactions, and some not so natural. Factories and cars that burn fossil fuels send tons of pollutants into the air every day. The manufacturing processes for plastics release chemicals like chlorine, sulfuric acid and (in the case of PVC) vinyl chloride. Spraying aerosol cans, exhaling cigarette smoke and burning trash all decrease the level of our air quality.

Some of these pollutants are producing ground-level ozone. Others fall to Earth as acid rain, and some stay airborne to cloud the skies of big cities as smog.

There's no avoiding dirty air these days. Just going outside means inhaling molecules that our lungs would be better off without, and sitting in traffic -- well, if we all had air purifiers in our cars, our lungs would thank us. But what about the rest of our bodies? Surely the damage doesn't stop at our lungs when the activities of the lungs and the heart are so closely connected.

­In fact, medical science has long known that exposure to high levels of air pollution, especially particulate matter, can exacer­bate or even trigger heart disease. But until the last few years, exactly how this happened was ­a bit of a mystery. Now, researchers have uncovered some good evidence of air pollution hurts the heart.

In this article, we'll take a look at the evidence linking air pollution and heart disease. We'll examine how certain pollutants affect the cardiovascular system and see what we can do to minimize the risk of damage.

Let's start with a quick review of the cardiopulmonary (heart-lung) system to get an idea of how breathing polluted air into our lungs directly affects the heart.

This image of the air pollution over China might make anyone faint of heart.

Image courtesy of NASA

Particulate Matter and the Heart

­Our bodies can't run with­out oxygen. All of our cells need it, and they rely on our lungs and heart to deliver it.

Every breath we take brings oxygen into our lungs, and the lungs are the first destination for the blood pumped out by the heart. When the right atrium contracts, it squeezes blood into the lungs so it can pick up oxygen from the air there. That oxygenated blood then enters the left atrium, which sends it out to the rest of the body.

But what happens when there's carbon monoxide, particulates or sulfur oxides in our lungs right alongside the oxygen? The blood picks up that stuff, too, and it gets to the blood supply, the heart and to every inch of our bodies.

That's the problem: It's all connected. Unfortunately, the heart reacts just as badly to air pollution as our lungs do. While the main causes of heart disease are poor diet, family history, obesity, diabetes and smoking, there's increasing evidence that heart problems are significantly impacted by pollution. For instance, carbon monoxide from secondhand smoke decreases the amount of oxygen our blood can carry, which can starve the heart muscle of the oxygen it needs to work properly. Particulates in diesel exhaust can cause blood vessels to constrict, limiting blood flow.

These particulates appear to be especially damaging in terms of heart health.

Particulates are tiny bits of liquid or solid matter. When we talk about this type of air pollution harming the heart, we're usually talking about PM2.5 -- particulate matter that's less than 2.5 micrometers in diameter. That's roughly 1/10,000th of an inch, or about one-tenth the diameter of a human hair. These particles are small enough to get deep into the lungs. The American Heart Association reports a 1.4 percent increase in heart-related deaths for each 10 micrograms of particulates per cubic foot of air [source: AHA]. And 10 micrograms is not a lot. The U.S. Environmental Protection Agency (EPA) considers the low concentration of 35.5 micrograms (average over the course of 24 hours) to be acceptable for health purposes [source: GADNR].

­Some researchers have found that even those EPA-approved levels can cause damage to the heart and blood vessels, though, especially in people already suffering from heart disease. And now they might know why.

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Our hearts as well as our lungs have a hard time dealing with particulate matter -- like the pollution that hovers over Beijing.

ST-segment Depression and Pollution

­A recent study, published in 20­08, found a reason why hearts seem to react so badly to air pollution: Particulate matter can interfere with the heart's electrical system [source: Science Daily].

The heart muscle pumps blood by contracting, squeezing the blood within its arteries to force it into the rest of the body. Just like any other muscle, the heart's contraction is triggered by an electrical impulse. In the heart, the impulse is generated by the SA node attached to the right atrium. The rate and rhythm of this impulse determines the heart beat, or pulse (see What determines the rhythm of your heart? to learn more).

Harvard University scientists studied 48 heart patients after they left the hospital, and tested their heart function after having been exposed to Boston air after weeks and then months. What they found was a change in heart conductivity, called ST-segment depression. ST-segment depression is essentially a reduction in the heart's ability to conduct electricity.

Not only particulates but also black carbon, a general term describing traffic exhaust, was found to correlate with ST-segment depression. When levels of black carbon and particulates in the air increased, there was an increase in ST-segment depression among the test subjects.

What does this mean for those of us breathing polluted air?

The short of it seems to be that an already damaged heart is more susceptible to the effects. In people with atherosclerosis (clogged arteries), air pollution has actually been shown to speed the rate at which plaque builds up on artery walls. Still, while people with healthy hearts are less at risk for cardiovascular trauma related to air pollution, we all feel the effects. The AHA estimates that, on average, we could all be losing one to three years of life expectancy due to pollution-related heart issues [source: AHA].

The good news is, we can still do something to stay healthy while the world's governments slowly get around to fixing the air-pollution problem. We can all try to follow the guidelines given to heart patients: avoid heavy traffic when possible, stay indoors on the worst air-quality days, and, of course, get the heck out of L.A.

­For more information on air pollution, heart health and related topics, look over the links on the next page.